Re: [RFC PATCH 0/3] directed yield for Pause Loop Exiting

Balbir Singh
2010-12-14T09:25:35Z

* Rik van Riel <riel@redhat.com> [2010-12-13 12:02:51]:

> On 12/11/2010 08:57 AM, Balbir Singh wrote:
>
> >If the vpcu holding the lock runs more and capped, the timeslice
> >transfer is a heuristic that will not help.
>
> That indicates you really need the cap to be per guest, and
> not per VCPU.
>

Yes, I personally think so too, but I suspect there needs to be a
larger agreement on the semantics. The VCPU semantics in terms of
power apply to each VCPU as opposed to the entire system (per guest).

> Having one VCPU spin on a lock (and achieve nothing), because
> the other one cannot give up the lock due to hitting its CPU
> cap could lead to showstoppingly bad performance.

Yes, that seems right!

--
Three Cheers,
Balbir